Fountain pen



FIG. 1 is a left side elevational view of a writing instrument showing my new design, the right side being a mirror image thereof;

FIG. 2 is a front elevational view thereof;

FIG. 3 is a rear elevational view thereof;

FIG. 4 is a top plan view thereof;

FIG. 5 is a bottom plan view thereof;

FIG. 6 is an exploded left side elevational view thereof;

FIG. 7 is a point-end view of the body thereof.

The writing tip structure depicted by means of broken lines in FIGS. 6 and 7 has been shown for illustrative purposes only and forms no part of the claimed design. 

The ornamental design for a fountain pen, as shown and described. 